1. Field of the Invention
The present invention relates to an document reading device, more particularly to an document reading device which includes an automatic document conveying mechanism and reads plural documents one by one.
2. Description of the Background Art
An image forming apparatus such as an MFP (Multi function Peripheral), a facsimile machine, and a copying machine or a scanner apparatus includes an automatic document conveying mechanism such as an ADF (Auto Document Feeder). In the scanner apparatus (or automatic document conveying and reading mechanism) provided with the ADF, when plural documents are initially set on the ADF, document images can automatically be read by the scanner while the documents run one by one. In the scanner apparatus provided with the ADF, the ADF is incorporated in a document retaining cover that is openable in an upper portion of the scanner.
In reading images of the documents set in the ADF using the scanner, the document retaining cover is maintained in a closed state (retains the document) when the document passes by a read position of the scanner, and the document is brought into close contact with an imaging element, such as a CCD (Charge Coupled Device) and a CIS (Contact Image Sensor), which is located on a scanner side (flat bed side). Accordingly, when a user mistakenly opens the document retaining cover while the ADF conveys the document, the document departs from the imaging element, and the image cannot normally be read.
At this point, when the scanner includes a document retaining cover opening and closing sensor to always sense an opening and closing state of the document retaining cover, the document retaining cover opening and closing sensor can sense that the document retaining cover is opened even if the ADF currently conveys the document. Once the document retaining cover opening and closing sensor senses that the document retaining cover is opened, the document conveyance is immediately stopped to perform error handling.
However, in an inexpensive scanner that cuts cost, sometimes the scanner does not include the document retaining cover opening and closing sensor for the purpose of apparatus simplification and cost reduction. In such scanners, the opening and closing state of the document retaining cover cannot be detected while the ADF conveys the document, which results in a problem in that an abnormal read image is output.
In order to avoid the problem, for example, Documents 1 and 2 below propose a technology of determining the opening and closing state of the document retaining cover by analyzing image information obtained from an image sensor in a standby state of the scanner.
In the technology disclosed in Document 1 below, a white seal (white reference plate) is provided in a surface (a reverse side of the document retaining cover) on the document read side of a transmission frame, a signal level (white level) of light reflected from the white seal is obtained while shading correction is performed at the beginning of the image read, and the opening and closing state of the transmission frame is determined by comparing the signal level to a reference level.
Document 2 discloses the technology of detecting the opening and closing state of a cover of a document conveyance unit. Specifically, image detection information from the image sensor that detects an image based on the light reflected from the document is converted into binary information, the binary information is used as image read information in reading the image, and is used as information detecting the opening and closing state of the cover of the document conveyance unit at other times.
In a technology disclosed in Document 3, a detection plate in which two black lines are marked at a proper interval is attached to the backside of a document cover (document retaining cover), the marks are read by the CCD to sense the document retaining cover of the document cover immediately before the document is conveyed to the read position of the CCD, and conveyance means is stopped when the CCD senses that the document cover is in the opened state.
[Document 1] Japanese Patent Application Laid-Open No. 7-307844
[Document 2] Japanese Patent Application Laid-Open No. 9-200448
[Document 3] Japanese Patent Application Laid-Open No. 2003-344957
However, in the technologies of Documents 1-3, the opening and closing state of the document retaining cover or the like is determined before or after the image is read. Therefore, the opening and closing state cannot be detected when the user opens the document retaining cover while the image is read, which results in a problem in that an abnormality is generated in the scanned image.
Additionally, in the technology of Document 3, it is necessary to provide a dedicated member (detection plate) in order to detect the opening and closing state of the document cover, which possibly causes complicated apparatus and cost increase. Because the marks on the detection plate are provided in positions where the marks come into contact with other members, degradation and damage are generated with long-term use (permanent use), which possibly results in a problem in that detection accuracy of the opening and closing state is lowered.